1. Field of the Invention
The invention relates to techniques of projecting light onto a retina of a viewer, to thereby allow the viewer to perceive a display object via a virtual image, and more particularly to techniques of controlling presentation of images to the viewer to reflect a motion of the viewer.
2. Description of the Related Art
There are already known systems, as referred to “virtual retinal display systems,” for projecting light onto a retina of a viewer, to thereby allow the viewer to perceive a display object via a virtual image. See, for example, Japanese Patent Application Publication No. HEI 8-21975.
Typically, such systems are configured to include: (a) an emitter emitting light (e.g., a light source or the like); (b) a modulator modulating the light (e.g., an intensity modulator, a wavefront-curvature modulator, etc.); (c) a display unit outputting the modulated light to the retina of the viewer through an exit of the display unit, to thereby display in an image display region an image representative of a display object (e.g., a content or a group of contents, an object or a group of objects, etc.) in the form of a virtual image; and (d) a controller controlling the emitter and the modulator so that the image is displayed in the image display region.
One type of such display systems is a head-mounted display system having a display unit which is mounted on the head of a viewer in operation. One of conventional techniques of the head-mounted display system is disclosed in the above-mentioned Japanese Patent Application Publication No. HEI 8-21975.
A head-mounted display system may be configured to include a display unit for displaying a desired image with respect to the position of the display unit by treating the position of the display unit as a position reference for display. The thus-configured display system, in operation, enables a viewer to perceive a desired image at a fixed position without being affected by a viewer's motion, within an image display region (which is fixed with respect to the head position of the viewer).
That is to say, the above head-mounted display system operates the display unit to enable the viewer to perceive the desired image in fixed relation to the display unit, i.e., with a display position of the desired image being fixed within the viewer's field of view.
When the above head-mounted display system is also of a see-through type, a viewer is allowed to view a displayed image together a real outside world, with the displayed image being superimposed on the real outside world. If this head-mounted display system is configured, as discussed above, so as to allow the viewer to perceive the displayed image at a fixed position within the viewer's field of view, then the displayed image is fixed in position within the viewer's field of view, without being affected by a viewer's motion (e.g., changes in position of the viewer's body, movement of the viewer's head), within an image display region (which is fixed with respect to the head position of the viewer).
For these reasons, a viewer who essentially finds it natural that any images be viewed in fixed relation to a real outside world would feel unnaturalism in viewing a displayed image being formed in fixed relation not to the real outside world but to the view's field of view.
In contrast, a display system disclosed in the above-mentioned Japanese Patent Application Publication No. HEI 8-21975, is configured to display an image so as to allow a viewer to perceive the displayed image in fixed relation to a real outside world, in accordance with a relative position relation between the head position of the viewer and the real outside world.